An organic solar cell (organic photoelectric conversion element) has a power generation layer containing a p-type semiconductor and an n-type semiconductor on a transparent electrode, and a charge transport layer that transports generated charges to an electrode, and it has a configuration enabling that excitons formed by light absorption is charge-separated before deactivation and the generated charges are efficiently extracted to an electrode. In recent years, the efficiency has been significantly improved.
Further, as being producible by film formation of a solution containing organic substances using a simple method such as a coating method or a printing method, the organic solar cell is believed to be most appropriate for roll-to-roll mass production, and it is referred to as a next-generation solar cell that is expected to result in dramatic drop in cost compared to a solar cell of the related art.
However, compared to a crystal Si type solar cell or a solar cell consisting of a thin film of an inorganic semiconductor, the organic solar cell is still insufficient in terms of the power generation efficiency, and there is a problem that the aforementioned cost merit is not yet to be exhibited.
In addition, similar to a common organic electronic device (for example, OTFT or OLED), element lifetime of the organic solar cell is significantly impaired as it is affected by oxygen, moisture, and thus a barrier member (generally, a barrier film) which not allowing permeation of oxygen, moisture is needed. In particular, a problem is caused by incorporation of oxygen that lifetime of an organic solar cell is significantly impaired as an attenuation in short circuit current (Jsc) accompanied with decomposition of organic substances occurs according to continuous light irradiation.
In relation to the aforementioned problem, a technique of improving conversion efficiency by adding at least one alkyl-containing molecule with low molecular weight to a solution of a p-type semiconductor conjugate polymer and an n-type semiconductor fullerene is disclosed (for example, Patent Literature 1). It is known that, according to the effect by those additives, light conductivity and a charge transport property are improved by morphology improvement of a bulk heterojunction layer, which is formed of a p-type semiconductor conjugate polymer and an n-type semiconductor fullerene (hereinbelow, also referred to as a power generation layer). Further, a technique of obtaining even higher conversion efficiency by adding a specific aromatic compound having a hydroxyl group and low molecular weight followed by coating and drying is disclosed (for example, Patent Literature 2). By adding those additives to a coating liquid, aggregation state of a polymer or fullerene is generally controlled, and thus it is expected to form more preferable morphology.
Further, to lower the oxygen effect, a technique which is by adding 1,4-diazabicyclo[2,2,2]octane (DABCO) as a singlet oxygen quencher to suppress discoloration caused by oxygen is disclosed (for example, Non-Patent Literature 1).